1. Field of the invention
The present invention relates to a lamp device comprising a lamp tube, such as a UV lamp arranged in an outer globe having at least one opening which is closed by a socket through which there are electrical connections to the lamp tube. The invention also relates to a system comprising a lamp device and to a method of adjusting it.
Today, lamp devices for many purposes are known. Thus, for use in ultraviolet irradiation, it is known to use a mercury-dosed lamp arranged inside an outer globe and sealed in a socket, which is exteriorly provided with threads in order to be screwed into a corresponding socket for mounting.
Such UV intermediate pressure lamps are used inter alia in UV systems where it is important that the intensity of the ultraviolet light is sufficiently energy-rich, and that the wavelength of the radiation is reasonably uniform during the service life of the lamp. Such UV intermediate pressure lamps typically have a service life of about 1-3000 hours, following which they must be replaced. The termination of the useful life of the lamp is typically due to the lamp tube having become leaky.
When a lamp has burnt out, and it has been replaced, it is generally discarded as waste, even though it does contain some elements that could still be put to use. This disposal constitutes an environmental problem, as the lamp contains environmentally toxic materials. Such a disposal may moreover be considered to be a waste of resources since the lamp contains expensive materials. Pure quartz glass or synthetic quartz glass is expensive and cannot be molten down, as the quartz evaporates before it melts.
The lamp tube is dosed with mercury and/or other metals. Further, an inactive gas, such as argon or the like, has been added. In this connection, a distinction is made between low and intermediate pressure lamps.
These lamps are optimized to yield as much ultraviolet light as possible. Additional focus for the further development of UV lamps is the lamp power, at the same time as the lamps are made smaller and manufactured with a smaller diameter, in particular when low-pressure lamps are involved.
These trends, however, make the lamps more sensitive to temperature. It has thus been found that fluctuations in the surface temperature of a lamp results in a reduction in the service life and a great drop in the efficiency of the lamp.
In the manufacturing of a UV low-pressure lamp, the rated emission of the lamp is determined at a specific vapor pressure. In this connection, tests have shown that a change in the surface temperature of 5.degree. C. relative to the ideal surface temperature of the lamp may result in a reduction in the ultraviolet light (the electromagnetic radiation) in the form of both UV light intensity and change in the wavelengths of the light of 20%. This has turned out to be a problem in connection with UV lamps for disinfection of water or air as well as for inactivation of bacteria, virus, etc.
For intermediate pressure lamps in particular, the high burning temperature has the result that any joints in the lamp get leaky sooner or later, whereby air and water vapors penetrate into the lamp. Joints exist in lamps that are directly pressed together at the lamp ends in connection with the electrodes. This is seen clearly, as the gas of the lamp gets yellow or black, soon to be followed by the burnout of the lamp. A too low temperature of the lamp may cause the ionization covering to be deposited (condensed) on the inner side of the quartz lamp glass. This is seen in that the ends of the lamp become silver-colored.
Achieving and maintaining the correct surface temperature is particularly important in order to derive full benefit from the use of metal halide lamps, which are UV lamps which have been metal-dosed to achieve electromagnetic radiation within a specific range of wavelengths. This has been found to be a problem e.g. connection with UV lamps for photochemical processes where the wavelengths of the ultraviolet light may be decisive for the effect of the process relative to the individual substances.
A system of the prior art, developed for overcoming this problem, comprises a control system in which the tube voltage of the lamp is controlled by a light meter. The control operates in such way, that any decrease in the light intensity is detected by the light meter, which signals this to a control unit, which then increases the tube voltage of the lamp in order to compensate. However, an increase in the tube voltage also increases the surface temperature, which may rise to above the optimum level and enter a range, wherein the light intensity does not rise any further or, maybe, even decreases. This may prompt the control to call for still higher tube voltage, which may have the effect that the control will then contribute to additionally impairing the luminous efficacy of the lamp. Furthermore, also the service life of the lamp will be shortened.
2. Description of the Prior Art
U.S. Pat. No. 5,220,235 to Wakimizu et al discloses a lamp device where, in the outer globe, air is circulated through a socket for cooling. The UV radiation in the globe generates ozone, which is extremely toxic, and which moreover degrades the lamp, by way of the electrical terminals becoming oxidized. The outer globe is provided with a coating to retain harmful UV radiation, and is therefore this lamp is not of a type suitable for emitting a high output of UV radiation.
U.S. Pat. No. 4,963,783 to Grossman discloses an electroded mercury lamp for photochemical purposes. A sealed lamp envelope, which contains mercury vapor, is surrounded by an elongated quartz cylinder tube which defines a region for controlling a heat exchange medium which controls the temperature of the inner, sealed lamp envelope. The outer jacket allows for the use of a gas purge. Further, the outer jacket is designed to be demountable, in order to permit the interchange of different inner lamp envelopes. A tapered stopper is disposed at each end of the outer jacket and serves to guide and position an electrode lead through both the stopper and the outer jacket. The tapered stoppers also contain openings, which provide for an inlet and outlet stream of circulating heat transfer medium, which is preferably water.
Accordingly, it is an object of the invention to provide a lamp device that overcomes the above-mentioned drawbacks of the known lamp types. It is a further object of the invention to provide a longer service life for the lamp. Another object of the invention is to provide a system that ensures a longer service life and more constant luminous efficacy of the lamp tube, both as regards light intensity and the wavelengths of the emitted electromagnetic radiation.